Can a polypropylene sorbent sink?

NO! Only in rare cases a sorbent will float just beneath the water surface.

Cause:
- Surfactants in the water
- Dispersants in the water

If surfactants and dispersants are presents in the water then the surface tension changes in the sorbent, resulting in the sorbent then absorbing water and other liquids. The surfactant will cling to the polypropylene fibers resulting in the changing of the fibers surface tension. For further explanations on surface tensions, see chapter "Why does a polypropylene sorbent float and repel water".